1. Field of the Invention
The present invention relates to a push switch which is to be used in various electronic apparatuses, or an operating unit of an automobile or the like.
2. Description of the Prior Art
Basically, the structure of a push switch is configured by an operating portion and a switching portion. The operating portion is a portion with which a human hand is to be contacted, and has a function of transmitting an operation force to the switching portion. The switching portion is to be connected to a wiring board, and has a function of contacting and separating switch contacts. In such a push switch, in order to enhance the density on the board or the like, the switching portion is requested to be miniaturized. On the other hand, a part which is situated at the uppermost position of the operating portion, and which can be seen by and contacted with the human, i.e., a keytop is often requested to be enlarged (as compared to the switching portion) in view of operability and design. Many large keytops have a structure which is divided into a portion constituting an operating face, and a portion that supporting it from the lower side. Furthermore, the illumination type in which the operation state of an operated apparatus, or the like is illuminated and displayed on a keytop is often used. In the illumination type, the portion constituting an operating face is transparent and colorless or translucent, and an engraved plate or a color plate can be interposed between the portion and the supporting portion.
A push switch to which a large keytop is attached, and which is used for illuminating the interior of an automobile is configured in the following manner. A switching portion is formed on the side of the lower face of a cover in which a boss portion is disposed in the middle. A slider which is upward protruded from the switching portion is inserted into the boss portion in a vertically movable manner. A shaft portion which hangs from the middle of the lower face of the keytop is inserted into the boss portion in a vertically movable manner. A keytop returning coil spring is placed in the periphery of the boss portion and between the lower face of the keytop and the upper face of the cover, so that the contact/separation state of switch contacts is switched over by a pushing operation, but the keytop is always returned to the state attained before the operation.
Such a conventional push switch is known in, for example, Japanese Patent Application Laying-Open No. 2004-273199. In the push switch, the axis of a keytop functions as the center of the switch, and a cover, a switching portion, and a keytop returning coil spring are placed coaxially with the keytop. In the switching portion, a slider is housed in a vertically movable manner in a box-like body in which the open upper face is closed by the cover, a slider returning coil spring is placed between the lower face of the slider and the inner bottom face of the body, a slider locking mechanism of the heart-shaped cam type is formed between one side face of the slider and the body, and switch contacts of the sliding contact type are formed between another side face of the slider and the body. Also the body, the slider, and the slider returning coil spring of the switching portion are placed coaxially with the keytop.